Radio frequency amplifying system



Oct. 6, 1931. L. L. JONES RADIO FREQUENCY AMPLIFYING SYSTEI Fil y 1926 3 Sheets-Sheet l v%% ATTORNEYS Oct. 6, 1931. 1.. 1.. JONES 5 5 RADIO FREQUENCY AMPLIFYING SYSTEII Filed J ly 19, 1926 3 Sheets-Sheet 2 IAF DET

INVENTOR Lesrer LJones ATTORNEYS Oct. 6, 1931. 1.. L. JONES RADIO FREQUENCY AMPLIFYING SYSTEM 3 sheets -sheet 3 Filed July 19, 1926 Patented Oct. 6, 1931 LESTER- L. JONES, F ORADELL, NEW J ERSEY RADIO FREQUENCY AMPLIFY'JING SYSTEM Application filed July 19, 1926. Serial No. 123,346;

This invention relates to radio receiving apparatus, and more specifically to aradio frequency amplifying system; and has special reference to the provision of an improved method of and means for controlling the signal volume in radiofrequency receiverswithout'afi'ecting the selectivity of the receiving setgthe quality of the received signal or the tuning of the system. a

The present invention is especially directed to a method of and apparatus for varyingv the. radio frequency voltage amplification'or gain inradio receiving systems for avery wide-rangesuch as 5,000 to 1 so as to us properly provide for the very wide range of signal input voltages encountered in the operation of radio receiving set-s especially for use in thereception of radio broadcast, transmissions. a I I B0 A number'of methods have heretofore been devised: and'used for-controlling the signal output or amplification of radio frequency circuits. The method most commonly employed and-which is especially applicable to receiversof the radio frequency amplifying type is tovary the radio-frequencyamplification byvarying the tube filament heating current as by a: rheostat' in series therewith This-method is especially applicable to tuned'radio amplifiers in which theinput and output'circuits are electrically decoupled,-as forexample inthe system shown in my copending application Ser. No; 607 ,046, the divisionalapplications of which-are now Patent Nos; 1,658,804 and 1,658,805 granted February 14, 1928. This method, although widely in use at the present time, isobjectionable since-there is a tendency to introduce disturbances and distortions on strong signalswhen the electron flow is greatly reduced on account of the sharp upper limit to the electron flow which tends to cut off the high amplitudes: Anotherobjection to this method is that the system is not Well adapted for use with rectifying apparatus generating a direct currentrfrom alternating powersupply lines for heating the filament and sup plying the space current (the so-called A battery eliminators) since the variation of filament and: space current incident to the use "ill disturbances may be brought'in, and second-- ly because when the circuitis detuned slightly. distortion of the signal mayresult, for then it resonates more strongly to the radio frequencies corresponding to the carrier Wave modulated at the higher voice frequencies; and this has the efi'ect' of suppressing the low audio frequencies and increasing the relative amplitude of the higher audio fre-' quencies. It has also been attempted to control the volume by varyingthe audio frequency amplification as by means of a potentiometer connected With the input of the audio amplifier system. This latter method has the disadvantage of overloading andsaturating the detector when the signal is strong, with consequent distortion of the signal;

Another method'employed in the early art for the reception of telegraphic code signals was to provide a variable coupling (either capacitive or magnetic) between'the antenna and-the tuned input circuit of'the detector or radio frequency amplifier. This method is practical butis limited in the range of variation practically obtainable, on account of the unavoidable residual couplings at the minimum. With thismethod there is, also a tendency to cause detuning of the coupled circuits when the coupling is adjusted to wards a maximum signal and the method is not easily applicable to receivers using the loop type of receptor.

In. accordance withthe principles of my present invention I depart from the abovestated methods and b means of my present invention the diificultles referred toabove as found incidentto the use of prior methods are eliminated and a range of volume variation is obtained without introducing any fine coupling balance.

lhe principles of the invention and the many advantages thereof may be best understood by reference to the accompanying specification and drawings forming part thereof, in which:

Fig. 1 is a wiring diagrammatic view of a radio receiving system embodying my invention and showing six cascaded stages of radio frequency amplification,

Fig. 2 is a wiring view of a radio receiving system showing my invention applied to sin stages of cascaded untuned amplifiers,

Fig.3 is a modification of my invention applied to a tuned radio frequency receiver of the conventional type without means for neutralizing interstage feedback reactions.

Fig. i is a still further modification thereof showing the invention applied to a tuned radio frequency receiver employing a means for neutralizing for adjacent stage feed-back reactions. and

Figs. 5 to 7 show three different methods of variably coupling the cascaded stages to carry out the principles of my present 1nvent-ion.

Before describing my invention in detail I will briefly point. out, by reference first to Fig. 1 of the drawings (which figure shows a cascade amplifier system built in accordance with the principles of my invention as disclosed in my copending application Ser. No. 92.761 filed March 6. 1926. now Patent No. 1.620.661 granted March 15. 1927), that my invention comprises in its generic aspects a I cascade amplifier system the stages of which are interlinked or coupled by transformers such as T and T having inductively coupled primaries and secondaries P S and S. the coupling between which is varied over a wide range to control the signal volume of the system. the construction and arrangement being such that the coupling of the transformers is varied without changing or altering the tuning of the system. To accompli sh the intended results in the preferred manner. the mutual inductance range of a transformer such as T is of the order of 50 to 1: and for the purpose of producing the desired. range of radio frequency voltage amplification for the whole system, the coupling between the primary and secondary windings of a plurality of the transformers such as T and T is varied, producing there by a ran ge of volume variation which is the geometric product of the range of volume a.- riation of each coupling transformer. Desirably the coupling of the plurality of transformers is effected by means of a single control element designated in the drawings as coupling control, the primaries P and P being associated together to be operated by the single coupling control element, as indicated by the arr-owed and dotted lines in Fig. 1 of the drawings.

As will become clearer hereinafter, the constants of the inter-related circuits are so chosen and predetermined that the geometric variation of volume or amplification is obtained by this coupling system of my invention without appreciably detuning any of the circuits so that the volume control is made independent of the tuning controls and without changing the selectivity of the receiving set or the quality of the received signals over the whole wave length range over which the circuit is tuned. By the means hereinafter described, the range of 50 to 1 in mutual inductance is secured for each coupling stage so that the total range obtainable with two stages would be 2500 to 1 and with three stages 125,000 to 1. Although these figures are based on the range of mutual inductance variation, it will be understood that they also correspond approximately to the range of voltage variation obtainable at the input of the detector at any given frequency.

A few of the advantages flowing from this method of controlling the volume of the system may now be given to aid in further understanding the underlying principles thereof and the manner by which I depart from prior methods with the use of this coupling system. A prime desideratum in radio frequency receiving systems centers about the provision of a system having a large range of volume variation because of the correspondingly great variation of signal voltage received in the antenna or loop due to variations in transmission, variations in distances between the receiver and the various stations that might be received, as well as the great range of receptivity characteristic of different receiving locations, which latter factor compounds geometrically with the preceding two factors. I have in mind for example, the 100 to 1 difference in receptivity between loop receivers in suburban homes as against similar receivers in the interior rooms of steel frame apartment buildings, or in the corresponding range of receptivity between outdoor antennae generally above the level of surrounding structures and those which are shadowed by higher steel bridges or buildings.

Another desideratum in radio frequency systems, as was pointed out in my copending application, Ser. No. 716,214, filed May 27. 1924, now Patent No. 1,712,214 granted May 7 1929, centers about the provision of means for varying the coupling between the circuits simultaneously with the tuning thereof since the coupling values between transformer windings to secure maximum amplification vary for different frequencies. It is also a desideratum that the separate controls for amplification should not detune or impair the selectivity of the variousc'ircuits, nor shouldthey cause changes in the plate and filament supply currents,'especial ly when such currents are supplied from rectifying apparatus whose terminal voltage is variable with variable current drain. As far as I am aware, the method of controlling the amplification over a large range meeting these conditions has not been designed prior to my present invention.

' The present invention possesses the ad vantage of meeting these difiiculties in a very simple way. The broadcast listener receives various signals having a wide range of intensity as he tunes from one station to another. lVhere the received signal is strong the couplings are adjusted for relatively low values so as to give the proper voltage input to the detector. lVhere a station is heard relatively weakly due to its extreme distance or to other transmission difiiculty, an adjustment of the volume control for a louder-signal automatically leaves the operator with that coupling giving the maximum efficiency for that frequency. The receiver operator therefore automatically adjusts with one and the same control for suitable volume on all stations-including the strongest and for maximum efficiency on all'weak station's,and so combines the functions of the predetermincdly combined wave length and coupling variation, and the wide range volume control. 7

This advantage of adjusting the e'fiicienc-y of the amplifier for the band of frequencies it is desired to receive ;may be very-marked when the amplifiers are of the untuned type designed to operate over a large frequency band, as for example, a 3' to 1 band. In such case, especially on the shorter wave lengths, with the best designs'thus' far produced there is a considerable variationof efficiency over the ent -e frequency rangein each stage, and this efi-1ciency variation compounds geometrically so that for a sensitive receiver having four or more stages of untuned amplification the total variation may be quite considerable. The adjustment of couplings in transformers of this type have not heretofore been attempted and this may be accounted for by the complexity of control that would have resulted without em ploying the principle of my present inven tion, whereby these variations are related with the necessary volume control to produce the maximumsimplicity of operation.

I will now describe my invention more in detail, first as applied to Fig. 1 of the drawings. In this figure I show radio frequency system embodying six stages ofiradio frequency amplification designated 1 R. F. to 6 R. F. and a stage of detection designated Dot, this being connected either to the telephones or to an audio-system'of'one or more stages in a manner well known in the art. Each of the stages comprises an electron dis charge tube having the filament grid and plate electrodes designated f, g and p with suitable-exponents corresponding to the position of the tube in the series, the filaments being connected to the A battery designated A in a manner wel'lknownto those skilled in the art and as shown in F ig. 1 of the drawings, and the grid and plates being arranged in input and output circuits designated 2 and o with exponents corresponding to the position of these circuits in the cascaded system. The system is also employed with a receptor of the loop type designated 'L connected to the first input circuit 1;; and the system is tuned by adjustable condensers C, C and C placed in the input circuits 1" and i in the first and third radio frequency stages.

In this system shown in Fig. 1 of the drawings, I cascade 'untuned and tuned radio fre-' qucncy stages, and to this end'the tubes 1 R. F. and 2 R. F. are coupled together by nontunable means which comprises a coupling inductance L' common to the coupled circuits 0' and 6 the input circuit 6 also including-afixed condenser K in series with the coupling inductance L of the order of magnitude of .001 microfarads. To neutralize both adjacent and distance stage feed-backs as pointed out in =myaforesaid copending application Ser. No. 93,761, the untuned coupled circuits 0'-z"- are constructed so that the natural frequency thereof is greater than the highest frequency through which the input circuit 5 is tunable,and the oscillation-creating feed-back reaction thereby produced is neutralizedover the whole wave length range by the provision of a resistance R" of a magnitude such that it functions for producing a feedrforward of energy from the input circuit z" toithe output circuit 0' to neutralize the feed-back reactions, this resistance comprising about 2,000 ohms, which resistance'is preferably inductance and capacity-free. Preferably also an intermediate point-2 of said resistance is connected to the condenser K and for securing the optimum results this connection point should be such that the resistance common to. the output and input circuits should be from to of the whole resistance-R. J

The third and fourth radio frequency stages are coupled to each other i-na manner similar to that shown for thefirst and second radio frequency stages. and such coupling means are designated by similar and appropriately primed reference characters. The fifth and sixthradio frequency stages 5 R. F. andG R. F. are coupled together'by means of a coupling impedance similar to L and a feed-forwardresistance R having a magnitude ofebout1500 ohms, the condenser K of the input circuit i being connected to the end of the resistance R and not to an intermediate point thereof.

These untuned coupled stages are coupled to each other by means of the transformers T and T' heretofore described, the primaries P and P of which are varied to vary the mutual inductance of the transformers over a wide range such as over a range of to 1, both primaries being preferably operated by a sin 'le control unit designated coupling control". The filament circuits F, F etc, of the coupled radio frequency stages are provided with non-variable resistances 7*, 7*, etc., so that the volume control or variation of amplification of the system is not varied by changing the filament current but is varied only by the control of the mutual inductances of the transformer. The mutual inductance variation is effected without producing any appreciable change in the tuning of the system and to accomplish this the primaries of the transformer should have a relatively high resistance across the same coupled with substantial absence of capacity across the primaries. The primaries are of the untuned circuit type the natural frequency of which should be equal to a frequency higher than the highest frequency of the range of the system. Capacities across the primary should be avoided for such capacities would vitiate the result because the decrement would be so reduced as to make the prin'iary periodic and therefore capable of changing the tuning of the system with the variation of the coupling. The system is so designed that the self-inductance in the primary or plate circuits is not varied, since a variation thereof. especially where no neutralizing means is provided, would produce changes in regeneration and hence in the selectivity of the input, which would be especially objectionable. in multi-stage receivers since the selectivity geometrically increases with the stages. By means of the coupling variation described and shown in the drawings, I am enabled to maintain the selectivity substantially constant over the whole wave length, as well as to prevent the change of tuning by any appreciable coupling adjustment.

The last radio frequency stage 6 R. F. of the system shown in Fig. 1 is connected to the detector tube Det. by means of a non-tunable transformer T having the primary P and secondary S, the output detector circuit 0 being connected to the audio system as indicated. The detector may be provided with the usual grid leak g.l.; and across the pri mary P is preferably connected a fixed condenser K of the value of 20 mmfds.

Referring now to Fig. 2 of the drawings, I show the principles of my invention applied to a six-stage cascade system of untuned amplifiers designated respectively 1 R. F. to 6 R. F., the same being connected to a detector Det. followed by a stage of audio amplification 1 A. F. which in turn is connected to the loud speaker or telephone Tel., the system being employed with a loop receptor L. The first and second radio frequency stages 1 R. F. and 2 R. F. are coupled together 1) the coupling impedance L in series wit feed-forward resistance R to the end of which is connected the condenser K while the remaining stages are coupled to each other by means of the untuned transformers T -T having correspondingly numbered primaries and secondaries. Across the primary P there is provided a condenser of the order of 20 mmfds; and the coupling between the primaries and secondaries of the transformers T ",T,; inclusive is varied to effect the volume or amplification variation, as indicated by the arrowed lines in Fig. 2 of the drawings, the same being simultanenously effected y means of the coupling control connecting as shown in dotted lines all of the transformers T T Vith reference to the untuned amplification system shown in Fig. 2 of the drawings, I am aware that it is old in the art to vary the constants of the untuned transformers separately or in combination. This variation of the prior art, however, was in the nature of a tuning adjustment and it was effected by introducing a variable amount of iron into the core of the coils without, however, changing the geometric relations between the coils, this iron tending to change the frequency of the natural vibration of the transformer windings so as to improve the amplification at different waves. The improvement resulted, however, from the resulting correspondence of transformer frequency with receiver frequency, and therefore was more of a tuning adjustment than a volume control. This method of the prior art was also insufficient as a volume control because at some band in the wave length range the variation of amplification secured by the variable iron core was too limited an amount. The system in which my present invention has its greatest value is, moreover, one in which the tuning circuits have approximately constant damping, preferably their own natural damping, and in which these tuning circuits are substantially free from tube feed-back reactions. In such a system the desirable condition of constant and predetermined selectivity of the tuning circuits precludes the use of a volume control which concommitantly varies the selectivity through regeneration. In the system shown in Fig. 2, the tuning is effected by means of the tuning condenser C and the neutralization of feedback is obtained by coupling the first two stages in the manner described.

In the modification shown in Fig. 3 of the drawings, I show a tuned type of radio frequency receiver having two radio freplished by means of the tuningcondenser G,

C and in the input .circuitsoi the radio frequency andjdetecting stages, the first input. circuit being, connected to the loop receptor Ii. The stages arev coupled together by the, two transfo'rmersT, Teach having the primaries and secondaries P and S, the couplings of. both transformers being multaneouslyeffected by adjusting in unison the two primaries P, P by means of the coupling control? as diagrammatically} indicated in 30f the drawings, In Fig. 4 of the drawings I'show my in vention applied to a timed radio frequency system of, the type shown in Fig. 3 with capacitive neutralization provided to neutralize the adjacent stage feed-back reactions, the

parts of the system shown in Fig. 4 which are similar to those shown in Fig. 3 being designated by similar reference characters. The primaries of'the transformer-ST, T each comprises, however, the connected plate and compensating coilsL and'L the compensatingcoils L being each connected to the grid of: the radiofrequency stages through the compensating: condensers C Asindicated, itiis; necessary to'provide asymmetricalvariation of the-reactions of the tuned circuits ofthe plate coil L and the. compensating coil L The-main reactingvoltages on the-plate and compensating condenser arise from the reaction of.the tunedcircuit on L and L and if this reactionis unbalancedduring the coupling variation, the resulting feed-back at some adjustment may be sufficient to seriously vary the selectivity of the preceding, tuned circuit. or even to create objectionable oscillations. The primariesofthe transformer are here also connc'cted to be operated 1 in unison by the coupling control.

In order to getthe large range of variation andampl-ification of my coupling controlsyste-m, it is necessary, especially in a single stage of amplification, to varythe coupling over a wide range. such as a 50 to. 1 range. Preferred methods ofsecuringthislarge range of coupling variation are shown in Figs. 5 to 7 of the drawings, which I willnow describe.

In Fig. 5 I; show a transformer having a simple solenoidsecondary S witha primary P'rotatable'through'an angle of at least 90 and preferably at one end of the. secondary S, said primarybeingrotatable aboutan axis 0, the angleof adjustment beingindicated by the arrowed linein saidfigure. The manner of. connecting the primaryand secondary in circuit with the groundingofone end of the secondary is also clearly indicatedin said r figure.

In Fig. 6 of the drawings I show a transformer having a solenoid secondary coil which is partially astatic magnetically, this coil comprising the two halves S and S each having the same number of turns and separat ed a distance Z approximately. equal. to the diameter of the coils. The coils are wound in opposite directions and have a-self-inductance approximately 20% lessthan the sum of the 'self-inductances of. the two halves alone. The primary coil P is asimple short solenoid of larger diameter than the secondary and is arranged to pivot on the axis 0 and swing through the are indicated by the arrowed line X, Y in the figure. In the position OY the coupling is at aminimum (substantially zero) because the primary couples equally and differentially with the two halves of the secondary. In the position OK the primary has a maximum coupling with the secondary, since the couplingto the section S is a maximum and the reverse coupling to the section S is substantially zero. The

manner of connecting the primary and secondary windings to the adjacent tubesis also indicated in this figure.

In Fig. 7 of the drawings I show a coupling a 'iparatus very suitable for my volume variation, the same being shown used with the magnetically and capacitively self-shielded secondary coils disclosed in my copending application for coil system, Ser. No. 111,074, filed 22, 1926, now Patent No. 1,608,560 granted November 30, 1926. The astatic secondary system consists of the two oppositely wound solenoids S S which are related as described in the aforesaid application. The primary coil P is a relatively short solenoid having a diameter slightly less than that of the inner coil S The primary is arranged to slide in andout of the low potential end of the inner coil by some such'means as illustrated in the figure. The coil is here shown pivoted about an axis 0 so that it can swing thru the arc ABC. The coupling variation, as the coil moves from its inner position C to its outer position A, is very rapid because of the astatic nature of the secondary combination. Variation of coupling in this system by the rotational method shown in Figure 5 is more difiicult, on account of the larger clearances required around the primary coil. It is most diflicult to secure sufiiciently tight coupling to this astatic system; so that the clearances between the primary and the inner coil, must be reduced to a minimum. In fact, I have foundtthat this method of coupling is the only method of securing any substantial mutual inductance between primary and secondary.

In all the methodsshown in the preceding figures it is necessary for the perfect operation of my system to arrange the parts so that the variation of coupling does not cause any substantial variation of tuning in the secondary system. For example, the primary coil should be close only to the ground end of the secondary, so as to avoid building up capacitive shunts across the secondary coil by reason of the capacity between the primary and secondary windings. In the form shown in Figure 6 for example, there is little capacitive change in the maximum position because the primary coil is over the ground half of the secondary. In the minimum position the capacity between windings is small because of the edge presentation of the primary coil in the plane thru the axes of the coils, and because of the relatively large spacing between the winding sections in the plane thru the secondary coil axis and parallel to the axis of rotation O.

The coil system shown in Fig. 7 is preferred for use in a multi-stage amplifier. The astatic nature of the secondary coils eliminates troublesome feed-back couplings between a plurality of secondaries. The small size primary coils minimize energy transfer to distant circuits by the magnetic fields due to currents flowing in the plate circuits.

The manner of making and using radio frequency systems embodying the principles *2 of my invention and the many advantages thereof will in the main be fully apparent from the above detailed description thereof. It will also be apparent that while I have shown and described my invention in the preferred forms, that many changes and modifications may be made in the structure disclosed without departing from the siirit of the invention, defined in the following claims.

I claim:

1. In a cascade system embodying a number of stages interlinked by a plurality of inductively coupled transformers, the method of varying the degree of energy transmission in the system to control the signal volume thereof which consists in conjointly varying the coupling between the primary and secondary windings of a plurality of the transformers producing thereby a range of volume variations which is the geometric product of the range of volume variation of the separate coupling transformers.

2. In a radio cascade system embodying a number of stages interlinked by a plurality of inductively coupled transformers certain of which stages are adjustably resonant to a received frequency, the method of varying the degree of amplification of the system to control the signal volume thereof which consists in varying the coupling between the primary and secondary windings of a plurality of the transformers producing thereby a range of volume variation which is the geometric product of the range of volume of the order of 50 to 1 to control the signal volume of the system.

4. A cascade amplifier system comprising a plurality of stages at least one of which consists of an amplifying tube stage, a transformer coupling said tube to a subsequent H stage, the primary of the transformer being in the plate circuit of the tube and said plate circuit being untuned, and means for varying the coupling between the primary and the secondary of the transformer, the constants of said coupled stages being such that the variable coupling means may be adjusted without appreciably changing the tuning of the system and over a substantially wide range to control the signal volume of the system over a substantially wide range.

5. A cascade amplifier system comprising a plurality of amplifier stages, means interlinking said stages including a plurality of inductively coupled transformers, and means for varying the coupling between the primary and secondary windings of a plurality of the transformers for producing a range of volume variation which is the geometric product of the range of volume variation of each coupling transformer.

6. A cascade amplifier system comprising a plurality of amplifier stages, means interlinking said stages including a plurality of inductively coupled transformers, means for tuning the system, and means for varying the coupling between the primary and secondary windings of a plurality of the transformers without varying the tuning of the system and for producing a range of "olume variation which is the geometric product of the range of volume variation of the separate coupling transformers.

7 A cascade amplifier system comprising.

a plurality of amplifier stages, means interlinking said stages including a plurality of inductively'coupled transformers, means for tuning the system, and means for varying the coupling between the primary and secondary windings of a plurality of the transformers without varying the tuning of the system and for producing a range of volume variation which is the geometric product of the range of volume variation of the separate coupling transformers, the mutual inductance range for eachtransformer being I of the order of-50 tol.

for transferring energy in one circuit to a circuit next ad acent thereto, and means for eonjointly adjusting a plurality of said adjustable coupling means for producmg a range of energy transfer variation for the system which is the geometric product of the range of energy transfer variation of the components of said plurality of coupling means.

9. A radio amplifier system comprising a plurality of electron discharge tube circuits arranged in cascade or series, a plurality of adjustable coupling means linking the said tube circuits together in series, the circuits and coupling means being such that each of the said coupling means is effective for transferring energy in one circuit to a circuit next adjacent thereto, and means for conjointly adjusting a plurality of said adjustable coupling means for producing a range of volume variation for the system which is the geometric product of the range of volume variation of the components of said plurality of coupling means.

10. A radio circuit system comprising a plurality of circuits arranged in cascade or series, certain of said circuits being adjustably resonant to a received frequency, a plura'lity of adjustable coupling means linking certain of said circuits together, the coupled circuits and coupling means being such that each of the said coupling means is effective for transferring energy in one circuit to a circuit next adjacent thereto, means for conjointly adjusting a plurality of said adjustable coupling means for producing a range of energy transfer variation for the system which isthe geometric product of the range of energy transfer variation of the components of said plurality of coupling means, the said circuits having circuit constants such that the said coupling means is adjustable Without effecting any appreciable change in the resonance or tuning of the system.

' A 11. A radio amplifier system comprising a plurality of electron discharge tube circuits arranged in cascade or series, certain of said circuits being adjustably resonant to a received frequency, a plurality of adjustable coupling means linking certain of the said circuits together, the coupled circuits and couplingmeans being such that each of the said coupling means is effective for transfer-ring energy in one circuit to a circuit next adjacent thereto, and means for conjointly ad'ustin a )luralit of said ad'ustablc con- 0 a pling means for producing a rangeof volume variation for the system whichis the geometric product of the range of volume variation of the components of said plurality of coupling means, the said circuits having circuit constants such that thesaid coupling means is adjustable Without effecting any appreciable change in the resonance or tun- .ing of the systei 12. A cascade system comprising a plurality of circuit stages arranged in cascade or series atleast one of Which consists of an electron discharge tube amplifying stage, means for tuning the system to a received frequency, an adjustable coupling means coupling a plurality of said stages together, and means for'adjusting the coupling-means over a range of variation of the order of to 1 to vary the energy transfer between the coupled stages for producing a range of volume variation of the system, the constants of said circuit stages being such that the adjustable coupling means may be varied through its range Without appreciably affecting the tuning of the system. v

13. A cascade system comprising a plurality of circuit stages arranged in cascade or series at least one of which consists of an electron discharge tube amplifying stage, means for tuning the system to a received frequency, an adjustable coupling means coupling a plurality of said stages together, and means for adjusting the coupling means to vary the energy transfer between the coupled stages for producing a substantially Wide rangeofvolume variation of the system, the constants of said coupled stages being such that the adjustable coupling means may be varied Without appreciably affecting the tuning or selectivity of the system and over the substantially Wide range to control the signal volume of the system.

14. A radio circuit system comprising a plurality of stages arranged in cascade or series, a transformer embodying a primary and a secondary coupling one of said stages to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primaryand the secondary of the transformer for producing a substantially'wide range of volume variation of the system, the constants of the coupled stages including a natural frequency for the transformer primary Which is outside of the range of the frequency through Which the secondary stage is tunable and including a minimized capacityacross the said primary, the constants being such that the coupling between the primary and secondary may be varied through thesubstantially wide range Without appreciably affecting the tuning of the system.

15. A ItldlOCllCUltSYStGIIl comprising a plurality ofstagcs arranged 1n cascade or series, at leastone-of Which-consists of an electron dischar e tube, a transformer cm bodying a primary and a secondary coupling the tube stage to an adjacent subsequent stage, means for tuning the circuit of said adjacent stage over a range of frequencies, means for varying the coupling over a substantial range of variation between the primary and the secondary of the transformer for producing a range of volume variation of the system, the constants of the coupled stages including a natural frequency for the primary which is outside of the range of the frequency for which the secondary circuitis tunable, a minimized capacity across the said primary and an arranging of said primary adjacent .to the ground potential end of said secondary, the constants being such that the coupling between the primary and secondary may be varied through a wide range without appreciably affecting the tuning of the system.

16. A radio circuit system comprising a plurality of stages arranged in cascade or series, a transformer embodying a primary and a secondary coupling one of said stages to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primary and the secondary of the transformer over a substantial range independently of the adjustment of said tuning means for producing a range of volume variation of the system, the constants of the coupled stages including a natural frequency for the transformer primary which is greater than the highest frequency of the frequency range through which the secondary stage is tunable, the constants further including a coupling of the primary to said secondary so that a change of coupling between the primary and secondary of the transformer is unaccompanied b a change of capacity in the tuned secon ary stage, whereby the coupling between the primary and secondary may be varied for volume control through a wide range without appreciably affecting the tuning of the system.

17. A radio circuit system comprising a plurality of coupling transformers and a plurality of tunable stages each having the construction set forth in claim 16, the con plings of a plurality of transformers being conj ointly adjustable.

18. A radio circuit system comprising a plurality of stages arranged in cascade or series including at least one electron discharge tube amplifier, a transformer embodying a primary and a secondary coupling one of said stages to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primary and the secondary of the transformer over a range of variation of the order of to 1 independently of the adjustment of said tuning means for producing a range ofvolume control variation of the system, the constants of the coupled stages including a natural frequency for the transformer primary which is greater than the highest frequency of the frequency range through which the secondary stage is tunable, the said primary being adjustably coupled to the low potential end of said secondary so that a change of coupling between the primary and secondary of the transformer is unaccompanied by a change of capacit in the tuned secondary stage, whereby coupling between the primary and secondary may be varied through a wide range without appreciably affecting the tuning of the system.

19. A radio circuit system comprising a plurality of stages arranged in cascade or series, at least one of which consists of an electron discharge tube, a transformer cmbodying a primary and a secondary coupling one of said stages to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primary and the secondary of the transformer over a substantial range independently of the adjustment of said tuning means for producing a range of volume variation of the system, the constants of the coupled stages including a natural frequency for the transformer primary which is greater than the highest frequency of the frequency range through which the secondary stage is tunable, the said primary having a minimized capacity thereacross, and being coupled to the low potential end of said secondary so that a change of coupling between the primary and secondary of the transformer is unaccompanied by a change of capacity in the tuned secondary stage, whereby coupling between the primary and secondary may be varied through a wide range without appreciably afltecting the tuning of the system.

20. A radio circuit system comprising a plurality of circuit stages arranged in cascade or series, means for tuning the system to a received frequency, coupling means linking the said circuit stages together, means for adjusting at least one of said coupling means over a substantial range of coupling variation to vary the energy transfer between the circuit stages coupled thereby for producing a range of volume variation at one point of the system, and means for conjointly producing a volume control variation at another point of the system to compound geometrically with the volume variation produced at said first point of the system.

21. A radio circuit system comprising a plurality of circuit stages arranged in cascade or series, means for tuning the system to a received frequency, coupling means linking the said circuit stages together, means for adjusting at least one of said coupling means over a substantial range of coupling variation to vary the energy transfer between thecircuit stages coupled thereby for producing a range of volume variation at one point of the system, means for additionally producing a volume control variation at another point of the system, and uni-control means connecting both of said volume control means for simultaneous operation.

Signed at New York city in the county of New York and State of New York, this 16th day of July, A. D. 1926.

LESTER L. JONES. 

